[PATCH] Mention NBD in migration.md

[Gregor Zattler]

Mention NBD as another possibility where a filesystem can reside on a
remote host, but is accessed through a local mount point.
---
 docs/migration.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/migration.md b/docs/migration.md
index b761686..990fc82 100644
--- a/docs/migration.md
+++ b/docs/migration.md
@@ -44,7 +44,7 @@ computer. e.g.:
 
 `/source` and `/destination` are paths that reside on the same computer.
 /source or /destination might be remote mounted filesystem like NFS or
-SSHFS.
+SSHFS or reside on a remote NBD.
 
 With this use case to migrate to the latest version, we recommend you to
 simply upgrade your existing installation of rdiff-backup “in-place”.
-- 
2.20.1